1. Field of the Invention
The present invention relates to a ceramic-forming composition, and a semiconductor porcelain substrate, a dielectric porcelain substrate and a capacitor that employ the composition.
2. Related Background Art
Semiconductor porcelains comprising an insulating layer formed at crystal grain boundaries have, in general, a large dielectric constant. It has been known to use such semiconductor porcelains to constitute capacitors having a large capacitance. Hitherto widely used as the semiconductor porcelains of this type have been porcelains mainly comprised of barium titanate. Such materials have a dielectric constant of as large as 70,000, but nonetheless have a dielectric loss (tan .delta.) of as large as 5 to 6% (1 kHz) and also a temperature variation of dielectric constant, of as large as 50% within the range of from -25.degree. to +85.degree. C. around the reference temperature of +20.degree. C.
On the other hand, known as porcelains that improve tan .delta. or temperature variation of dielectric constant of barium titanate are porcelains mainly comprised of strontium titanate. They are exemplified by a porcelain disclosed in Japanese Patent Publication No. 60-48897 as Sample No. 5, comprising 97.5 mol % of SrTiO.sub.3 as a main component to which 1.7 mol % of MnO.sub.2 and 0.8 mol % of Y.sub.2 O.sub.3 are added. This has a good tan .delta. of 0.6% and a good temperature variation of dielectric constant at -25.degree. to +85.degree. C., of within -7% to +6%, but has a dielectric constant of as low as about 51,000.